Sand injectites and its petroleum geological significances

Sand injectites and its petroleum geological significances

Liquefaction

Flow of fluids

Petroleum prospecting

Structural geology

Sand

Fluidization

Lithology

Sandstone

The good outcrops exposed along the California orogenic belt as well as successful exploration & development provide examples for the study of sandstone injections (injectites). Sandstone injections are widely developed in a variety of sedimentary systems from the Late Proterozoic to the Holocene of which deep-water systems are the most common ones. The lithology of injection is more frequently fine to medium-grained sandstone in turbidite fans, and the host layers are mainly mudstone and shale. Sand injections are comprised of 4 components including parent units, host strata, sand intrusion/extrusion, and the fracture systems and 5 types of sand dikes, sand sills, and columns/sand pillars, sand volcanos and injection complexes. The geometries of sand injection mainly consist of 3 types like saucer-wing shaped, conical shaped and crestal complex, and the top of the intrusion often develops mound shape. The interior part of sand injection is often structureless or laminated, with erosion boundaries and mass mud clasts, like a jigsaw. The formation conditions of intrusion include unconsolidated sand body, low-permeable overlain layers, pore fluid overpressure and dominant channel of the sand body. Seismic liquefaction, disequilibrium compaction, overburden, regional tectonic stress, and fluid flow are the most common triggering mechanisms. The formation process of intrusive body includes 5 processes:pore fluid overpressure, sand liquefaction, hydraulic fracturing and fluidization, sand injection and redeposition. Sand injections increase reservoir volume, link sand bodies together like conduits, and form injection traps. Sand injections can also be used to predict regional stress fields, but may also lead to failure of seals and water channeling. The determination of injecting time, geological process after injection and the deterministic study of triggering mechanisms are facing challenges. Interdisciplinarity, virtual outcrop, simulation experiments, and numerical simulation technology will be the future development direction. 2021, Editorial Office of ACTA PETROLEI SINICA. All right reserved.

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Shiyou Xuebao/Acta Petrolei Sinica

2021

Shao, Zhufu

Zhang, Wenxin

Mao, Cui

Luan, Xiwu

Zhong, Jianhua

Howell, John

Liu, Zexuan

Zhao, Bing

Ran, Weimin

Liu, Jingjing

journalArticle

2532697

10.7623/syxb202103011